The present invention relates to belts or straps such as, for example, elevator conveyor belts and, more particularly, to a method and device for splicing the ends of belts to either increase their length or to make the belts endless by joining the belt to itself in a manner which is reliable during operation and, while the device and process are described below for application to an elevator belt, it is understood that the device and process are not limited to this use.
One conventional method of splicing the ends of belts is hot splicing after the ends of the reinforcement material have been interlaced. Various forms of these hot splicing techniques are described in a number of patents, such as DE No. 1,165,354; FR No. 74.03141 and DE No. 907,996; FR Nos. 1,395,634, 1,582,190 and 1,440,605; and U.S. Pat. No. 173,686. One method is recommended in German standard DIN 22131. Another method is described in a paper entitled "Factors relating to vulcanized splice reliability for steel cord reinforced conveyor belting", Gozdeff, delivered to the 125th Meeting of the Rubber Division, American Chemical Society, in Indianapolis on May 8-11, 1984. Finally, an article entitled "A survey of present-day conveyor belt technology", H. P. Lachmann published in Bulk Solids Handling volume 4, number 4, December 1984, reviews the different technologies that can be used.
Examples of prior art hot splicing are illustrated in FIG. 1. There are however, conditions which make hot splicing techniques inapplicable such as for example, the length of a splice may be incompatible with the space available in the sheath or alongside the ele vator, or again the mechanical strength may become insufficient to guarantee trouble-free operation of the elevator if the temperature of the products transported or that of the gases circulating in the sheath is greater than 100.degree. C.
Specifically, in the case of interlacing of metal cords, the two ends of the belt(s) are bonded together by the rubber mixture separating the ends of the cord(s). It is known, however, that as the temperature increases, the mechanical properties of elastomer-based mixtures decrease; the same applies to the bonding forces between the rubber and the metal and, consequently, the tensile strength of such a splice decreases as the temperature rises.
Taking into account the risks encountered with a splice using hot adhesion and interlacing of metal cords, handling engineers have suggested replacing the adhesive bond with a mechanical bond designed to clamp the two ends of the belts(s) against one another. These techniques are referred to as "clip fastening", and are described in, for example, French Pat. No. 1,320,222 of as well as in advertising materials of specialized companies such as Goro or Flexco.
The compression force is exerted by metal flanges which are passed through by clamping bolts. The principle applied in mechanically splicing the ends of a belt or belts is theoretically more satisfactory than the hot-adhesion process, but an analysis of phenomena associated with operation of this type of device shows that there is only a slight improvement in operating reliability. This is because the lateral plates have a tendency to move away from one another as a result of the tensile force exerted on the two ends of the belt. To remedy this problem, two lines of bolts are generally used to clamp the plates, with the line of bolts placed closest to the tension zone being designed to limit movement of the plates.
FIG. 2, referring to the prior art in clip fastening techniques, explains the changes which occur during operation, in terms of distribution of pressure over the belt ends.
When the clip fastener is initially clamped, pressure is distributed uniformly over the entire extent of the two clamped ends. When operation begins, the lateral parts are displaced, which tends to decrease the pressure in zone X and increase that in zone Y. As a result of the increased pressure, the rubber mixture located in zone Y tends to be expelled and to flow, i.e. rubber is displaced from the most highly compressed zones towards those least compressed. The effect of this flow is to encourage the clamping plates to move closer together in zone Y, which accentuates the effect.
As confirmation of this analysis, it is commonly observed that the second line of bolts has completely loosened, which proves that the pressure effect exerted on the ends of the belt(s) is due not to the bolts but to a rotary movement of the clamping plates. Since the clamping force in zone X has decreased considerably, the strength of such a clip fastener consists only of the retention of the metal cords in zone Y and the frictional forces existing in zone X between the belt and each of the clamping plates. When zone Y is unclamped, an examination of the ends of the belt(s) in said zone shows that the tensile stress has been so high that there has been local destruction of the rubber mixture and of the bond between the rubber and the metal cords. This fact makes the strength of such a clip fastener very problematical, especially when this mechanical effect is combined with the effect of temperature, since it is well known that increased temperature accelerates and facilitates the flow of elastomer-based mixtures, and decreases the strength of the bond between said mixtures and steel cords.
To remedy this problem, it is possible to attempt to increase the pressure exerted by the lateral plates by locking the ends of the metal cords.
In, for example, Pat. DE No. 2,341,992 a solution, is proposed wherein each metal cord is stripped at its end of its rubber covering, and the end is inserted into a vise clamping device, Such a technique, time-consuming and difficult to implement, presents a further risk due to the design of the metal cord clamping zone and, if the clamping pressure is not properly controlled, there is a certain risk of cutting the metal cord, which would nullify the anticipated effect. In addition, the screws have a tendency to loosen under the action of vibration and temperature, and therefore require constant monitoring.
A different solution, used in particular to lock pretensioning cables in prestressed structures, involves stripping the ends of the metal cables, unstranding them, i.e. untwisting the constituent strands to spread out the end, and pouring around it a metal with a low melting point. This technique is highly reliable when it can be used, but pouring the molten requires that the clip fastener be placed in a vertical position, which implies either that one of the drums of the elevator can be moved, which is not always possible, or that the clip fastener can be placed at the top of the elevator, although pouring molten metal onto the ends of metal cables at a height of several dozen meters is tricky and even dangerous. In addition, such a device is practically non-removable, which does not facilitate maintenance of the elevator or replacement of the belt.
The aim underlying the invention, essentially resides in providing a fastening device for splicing a belt or belts, and more particularly belts which comprise reinforcement elements made of synthetic textiles or metal cords.
Other objects of the invention are the process of making splices using the device described, and application to a conveyor belt for a bucket elevator.
By virtue of the fastening device of the invention, it is possible to create, using a method that is as simple as conventional splices and is completely safe since there is no handling of hot products or adhesives or heating equipment, a splice between two adjacent ends oof two belts to produce a longer belt, or between the two ends of a single belt to produce an "endless" item ready for operation on a conveyor or elevator.
The device, of the present invention which requires only simple preparation of the ends of the belt(s) to be assembled, acts on the principle of a cable clamp by immobilizing the ends by a loop made around an upper rounded part of an intermediate plate of the fastening device, and by simple mechanical clamping of the belt reinforcement elements over the longest possible length and in a zone where the reinforcement elements are stripped of rubber to limit the risks of flow and the effects of tension and temperature.
Specifically, the fastening device of the invention comprises two lateral plates equipped with retainer irons as well as two intermediate plates having on their upper part a zone for winding the belt without folding or damaging the belt in order to form a loop and a lower part of which, in the form of an arc of a circle, facilitates winding of the belt under tension. A stop is provided against which the retainer iron is pressed during operation, and a central plate is also provided. The fastening device acts by simple mechanical clamping of the belt by the various component parts of the fastening device due to a provision of transversely extending bolts.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for the purpose of illustration only, several embodiments in accordance with the present invention.